Bipolar disorder (BP) is a serious psychiatric condition that affects 0.5 -1.5% of individuals in America. The age of onset of BP is during the initial childbearing years. Seventy percent of women with established BP will suffer recurrent episodes post-birth. Continuous medication administration is the mainstay of treatment for BP. Although the information available to physicians who treat pregnant women with unipolar depression has increased over the past decade, data to inform decisions about treatment of BP has not advanced similarly. Information about anticonvulsant use during pregnancy has been garnered solely from the study of women with epilepsy, who have increased risk for malformations independent of drug treatment. Data about atypical antipsychotic use in pregnancy is almost non-existent in either women with BP or schizophrenia. The majority of studies have not included the range of outcome measures that comprise the contemporary portfolio of the reproductive toxicity outcomes. Pharmacologists have produced data for altered physiologic states (renal or hepatic disease) and for other patient subpopulations (children and elderly). The need for similar studies in pregnancy is certainly no less than for these populations. New information must be obtained to guide risk-benefit decision-making to a new level of sophistication. This is a prospective observational study of women with BP during pregnancy and the mother-infant pairs n the first postpartum year. We plan to enroll 200 women with BP and 58 women without BP (for 140 and 40 completers, respectively). Decisions about treatment during pregnancy will be made by the woman with her physician (not associated with the study) prior to study enrollment. The major aims of the study are to define a cohort of pregnant women with DSM-IV defined BP and to: 1) Characterize the BP illness course in the population through pregnancy and the first postpartum year, with careful documentation of treatment(s) and gestational timing. 2) Evaluate function in the maternal role as well as occupational, educational and social domains. 3) Define pregnancy and infant outcomes in both medicated and unmedicated women with BP and compare them to those of unmedicated women without BP. Separation of the effects of medication from the disorder is critical to advance risk assessment. 4) Assess the infants'development through the first year of life. 5) Perform serum levels at 20, 30, and 36 weeks gestation to allow level/dose ratio monitoring for women who take medications during childbearing. The mother-infant serum levels of women with BP who breastfeed their infants also will be assayed. 6) Conduct pharmacokinetic (PK) studies on the subset of women who take lithium, the most common drug used to manage BP during pregnancy in our Center, at 20- 24 weeks, 32-36 weeks, and 12-16 weeks after birth. No such PK data are currently available.